Chapter 8: Environmental Health and Toxicology

The Environment is Out to Kill You

8.1 Environmental Health

• The global disease burden is changing • Infectious and emergent diseases still kill

millions of people • Conservation medicine combines ecology and

health care• Resistance to drugs, antibiotics, and pesticides

is increasing • Who should pay for health care?

Pathogens• Prions (Mad Cow, Kreuzfeld-Jacob)• Viruses (Ebola, AIDS, smallpox, common

cold, influenza, herpes)• Bacteria (cholera, typhoid, plague)• Protista (malaria, sleeping sickness, Giardia)• Fungi (athlete’s foot, yeast infections, Candida)

• Multicellular Organisms (tapeworms, trichinosis, schistosomes)

Prions

• Only known infectious agents without DNA• Misconfigured protein molecules• Bind to normal proteins and convert them to

misconfigured form• All known prion diseases attack the brain• No known cure; invariably fatal; very nasty

Viruses• Viruses are non-living but reproducing• Viruses invade cells and use cell reproduction

mechanisms to reproduce• Retroviruses permanently insert new DNA into

cell (AIDS)• Viruses cannot be attacked in cells• Being non-living, can’t be killed by antibiotics in

blood stream• Only defenses are immunization or prevention• Antibiotics do not work against viruses

Promiscuous Antibiotics

• Used improperly against viral infections• Essentially given as placebos• Sugar pills would be more ethical• Legitimate users do not use properly• Used as prophylactic measure in factory

farms• Creation of resistant micro-organisms• Waste antibiotics get into environment

8.2 Toxicology

• How do toxins affect us? • What Can You Do? Tips for Staying Healthy • How does diet influence health?

Chemical Hazards• Allergens (trigger immune response)• Neurotoxins (damage nervous system:

mercury, pesticides, lead)• Mutagens (alter genes) • Teratogens (cause birth defects: alcohol,

thalidomide)• Carcinogens (nickel, tobacco, radon)• Hormone mimics (PCB’s)

8.3 Movement, Distribution, And Fate Of Toxins

• Solubility and mobility determine where and when chemicals move

• Exposure and susceptibility determine how we respond

• Bioaccumulation and biomagnification increase concentrations of chemicals

• Persistence makes some materials a greater threat

• Chemical interactions can increase toxicity

8.4 Mechanisms For Minimizing Toxic Effects

• Metabolic degradation and excretion eliminate toxins

• Repair mechanisms mend damage

8.5 Measuring Toxicity• We usually test toxins on lab animals– “All that proves is rats shouldn’t smoke”– Reality: Animal tests predict human toxicity well

• There is a wide range of toxicity • Acute and chronic doses and effects differ• Detectable levels aren’t always dangerous– With enough equipment and money, we can

detect individual molecules

Response to Exposure

Response to Exposure

Chemicals in Concert

• Antagonistic (Vitamin A, E against carcinogens)• Additive (Effects combine)• Synergistic (Effects multiply: alcohol + drugs,

smoking + asbestos)• Sensitization or Desensitization

Factors in Toxicity• Chemical composition• Dose• Acute versus Chronic Exposure• Solubility and Mobility• Nature of exposure• Ability to metabolize, sequester, or excrete• Tendency to bioaccumulate• General Health

8.6 Risk Assessment And Acceptance

• Risk perception isn’t always rational• Risk acceptance depends on many factors• Some 1:1,000,000 Risks– Smoking 1.4 cigarettes (cancer, heart disease)– Two days in large city (air pollution)– 10 miles by bicycle (accident)– 1000 miles by jet (accident)– One chest X-ray (cancer)– 5 years on boundary of nuclear plant (cancer)– 100 charcoal broiled steaks (cancer)

Weapons of Mass Destruction

• Weapons capable of inflicting large numbers of casualties or affecting a large area in a single event

• Nuclear• Chemical• Biological• Any time you pack a large amount of

energy into a small space, you have a potential weapon

Chemical Weapons• Riot Control (Tear Gas)• Choking (Cl, phosgene CCl2O)• Blood (HCN)• Nerve (Sarin)• Blister (Mustard Gas)• Hallucinogens (researched, never used)• Incapacitating (researched, never used)• Defoliants (Agent Orange, Vietnam)

Chemical Weapons in War

• World War I– Tear Gas– Chlorine– Mustard Gas

• Japanese in China: 1930's - WWII• Not used by other parties in WWII• Yemen 1960's• "Yellow Rain:" SE Asia, 1970's (Discredited)• Iraq against Kurds, Iran, 1980's• US renounced first use but reserves right to

retaliate

Use of Chemical Weapons• Gases disperse too quickly– Usually delivered as aerosols– Dependent on weather conditions– Wind, rain, heat are unfavorable

• Most historical uses against unprotected targets– Trained soldiers have protection– Reduces efficiency of both sides– Psychological effect

Effects of Chemical Weapons• Nerve Agents– Long Term: Nerve Disorders, Brain Damage

• Blister Agents– Short Term: Severe Burns– Long Term: Skin Cancers and Lesions, Lung

Damage• Most Chemical Agents Easily Decomposed• Long Term Effects of Low-Level Exposure

Unknown– Gulf War Syndrome, Agent Orange

Biological Weapons• No known modern historical military uses• US has stated will not use• Limitations– Should be self-limiting– Need fairly quick action– Anthrax and Smallpox given most speculation

• Plant pathogens– Wheat Rust, Hoof-and-Mouth– Drug Interdiction?